This invention relates to delivery devices for implants placeable within tissue of the human body. Specifically, the invention relates to delivery of implants configured to aid in the restoration of blood flow to myocardial tissue of the heart. The invention includes a mechanism to monitor the position of the device and deliver drugs.
Tissue becomes ischemic when it is deprived of adequate blood flow. Ischemia causes pain in the area of the affected tissue and, in the case of muscle tissue, can interrupt muscular function. Left untreated, ischemic tissue can become infarcted and permanently non-functioning. Ischemia can be caused by a blockage in the vascular system that prohibits oxygenated blood from reaching the affected tissue area. However, ischemic tissue can be revived to function normally despite the deprivation of oxygenated blood because ischemic tissue can remain in a hibernating state, preserving its viability for some time. Restoring blood flow to the ischemic region serves to revive the ischemic tissue.
Although ischemia can occur in various regions of the body, often tissue of the heart, the myocardium, is affected by ischemia due to coronary artery disease, occlusion of the coronary artery, which otherwise provides blood to the myocardium. Muscle tissue affected by ischemia can cause pain to the individual affected. Ischemia can be treated, if a tissue has remained viable despite the deprivation of oxygenated blood, by restoring blood flow to the affected tissue.
Treatment of myocardial ischemia has been addressed by several techniques designed to restore blood supply to the affected region. Coronary artery bypass grafting CABG involves grafting a venous segment between the aorta and the coronary artery to bypass the occluded portion of the artery. Once blood flow is redirected to the portion of the coronary artery beyond the occlusion, the supply of oxygenated blood is restored to the area of ischemic tissue.
Early researchers, more than thirty years ago, reported promising results for revascularizing the myocardium by piercing the muscle to create multiple channels for blood flow. Sen, P. K. et al., xe2x80x9cTransmyocardial Acupuncturexe2x80x94A New Approach to Myocardial Revascularizationxe2x80x9d, Journal of Thoracic and Cardiovascular Surgery, Vol. 50, No. 2, August 1965, pp. 181-189. Although others have reported varying degrees of success with various methods of piercing the myocardium to restore blood flow to the muscle, many have faced common problems such as closure of the created channels. Various techniques of perforating the muscle tissue to avoid closure have been reported by researchers. These techniques include piercing with a solid sharp tip wire, hypodermic tube and physically stretching the channel after its formation. Reportedly, many of these methods still produced trauma and tearing of the tissue that ultimately led to closure of the channel.
An alternative method of creating channels that potentially avoids the problem of closure involves the use of laser technology. Researchers have reported success in maintaining patent channels in the myocardium by forming the channels with the heat energy of a laser. Mirhoseini, M. et al., xe2x80x9cRevascularization of the Heart by Laserxe2x80x9d, Journal of Microsurgery, Vol. 2, No. 4, June 1981, pp. 253-260. The laser was said to form channels in the tissue that were clean and made without tearing and trauma, suggesting that scarring does not occur and the channels are less likely to experience the closure that results from healing. U.S. Pat. No. 5,769,843 (Abela et al.) discloses creating laser-made TMR channels utilizing a catheter based system. Abela also discloses a magnetic navigation system to guide the catheter to the desired position within the heart. Aita U.S. Pat. Nos. 5,380,316 and 5,389,096 disclose another approach to a catheter based system for TMR.
Although there has been some published recognition of the desirability of performing transmyocardial revascularization (TMR) in a non-laser catheterization procedure, there does not appear to be evidence that such procedures have been put into practice. For example, U.S. Pat. No. 5,429,144 Wilk discloses inserting an expandable implant within a preformed channel created within the myocardium for the purposes of creating blood flow into the tissue from the left ventricle.
Performing TMR by placing stents in the myocardium is also disclosed in U.S. Pat. No. 5,810,836 (Hussein et al.). The Hussein patent discloses several stent embodiments that are delivered through the epicardium of the heart, into the myocardium and positioned to be open to the left ventricle. The stents are intended to maintain an open channel in the myocardium through which blood enters from the ventricle and perfuses into the myocardium.
Angiogenesis, the growth of new blood vessels in tissue, has been the subject of increased study in recent years. Such blood vessel growth to provide new supplies of oxygenated blood to a region of tissue has the potential to remedy a variety of tissue and muscular ailments, particularly ischemia. Primarily, study has focused on perfecting angiogenic factors such as human growth factors produced from genetic engineering techniques. It has been reported that injection of such a growth factor into myocardial tissue initiates angiogenesis at that site, which is exhibited by a new dense capillary network within the tissue. Schumacher et al., xe2x80x9cInduction of Neo-Angiogenesis in Ischemic Myocardium by Human Growth Factorsxe2x80x9d, Circulation, 1998; 97:645-650. The authors noted that such treatment could be an approach to management of diffused coronary heart disease after alternative methods of administration have been developed.
The present invention provides a delivery system for placing implants within tissue in the human body. The implant delivery system of the present invention provides several novel features, which are useful in delivering implants into tissue.
In one aspect of the invention a delivery device is provided that is especially configured to carry multiple tubular shaped implants at its distal end, engaging the implants by their inside surfaces. The delivery devices are inserted percutaneously into a patient and navigated to the site where the implant is to be located. The delivery systems of the present invention are particularly well suited for delivering implants into the myocardium to perform transmyocardial revascularization (TMR). Implants such as stents may be placed by the delivery device into the myocardial tissue to a proper depth to encourage revascularization of ischemic tissue. In such a procedure, positioning the implants into the proper depth within the myocardium is important to the success of the procedure because it has been observed that areas of the myocardium closer to the endocardial surface and to the epicardial surface are more likely to be responsive to revascularization. Additionally, spacing of the implants relative to one another in an area of ischemic tissue is important to the success of the revascularization process and avoiding undesirable side effects of placing foreign objects in the muscle tissue of the myocardium. Additionally, it may be desirable to deliver a therapeutic substance to the implant location, before, after or during delivery of the implant to promote revascularization activity such as angiogenesis. The features of the present invention address these concerns as will be discussed in greater detail below.
Reaching the intended implant delivery location with the delivery devices of the present invention first requires placement of a guide catheter prior to navigation of a deliverable catheter into the left ventricle. A steerable catheter that is placeable within the left ventricle and positionable in multiple locations with one catheterization is disclosed in U.S. application Ser. No. 09/073,118 filed May 5, 1998, the entirety of which is herein incorporated by reference. The delivery devices as described herein are insertable through the lumen of the delivery catheter and are extendible past its distal end to place the implants within the myocardial tissue. The delivery catheter provides directional control so that the delivery devices of the present invention can deliver multiple implants to a variety of locations within a given area of ischemic tissue.
In one embodiment of a delivery device of the present invention the device comprises a catheter having a compressible sleeve at its distal end which forms into a plurality of random folds when it is compressed, expanding its diameter and serving to capture the inside surface of any tubular object placed over it. The crinkle tube may be formed from a polymer such as polyethylene terephthalate (PET). The crinkle tube can securely retain tubular implants over its crinkled, radially expanded surface to a sufficient degree such that delivery into tissue does not push the implant off of the delivery device. Additionally, the crinkle tube catheter may be used in conjunction with an outer catheter shaft having a plurality of interior projections, which engage a plurality of implants in cue while the crinkle tube shaft delivers the implants from the distal end of the catheter sequentially.
In another embodiment, a tubular implant is maintained on the catheter behind an oval shaped segment of the catheter which presents a larger profile than the inside diameter of the tubular implant. A member slidable within the catheter engages the oval portion to deform it into a round shape, thereby permitting the implant to slip off the distal end of the shaft. Simultaneously with deformation of the oval to a circle shape, the inner member causes arms to protrude from the interior of the catheter and to engage the implant and push it in a distal direction so that it becomes implanted in the tissue. Additionally, the catheter has the ability to carry multiple implants over its shaft. The implants waiting in cue are also maintained in position on the shaft by a oval shape segment of the shaft that can be deformed to a circular shape thereby permitting advancement of the next implant.
In yet another embodiment of the delivery system, the delivery catheter comprises an elongate shaft that contains pressurized fluid within its lumen to motivate a plunger located at the distal end of the shaft and attached to a single implant attachment device. When fluid within the lumen of the delivery catheter is pressurized, the plunger moves from its position against proximal stops distally to its position against distal stops. That length of travel is sufficient to push the implant attached to the plunger into the intended tissue location. The benefit of the fluid pressure delivery system is a reduction in moving components needed to cause distal movement of the implant at the distal end of the catheter from the proximal end of the catheter, which is manipulated outside of the patient.
Another feature of the present invention includes a dual bladder drug delivery system, which may be associated with the delivery catheters discussed above. The dual bladder arrangement provides a first bladder, which contains a therapeutic substance near the distal end of the delivery catheter and a second bladder arranged near the first bladder so as to impinge upon the space of the first bladder when the second bladder is inflated. The second bladder is inflated with an inexpensive fluid simply to cause the evacuation of the first bladder, which contains a therapeutic substance to be delivered. The first bladder may be provided with a series of perfusion ports through which the therapeutic substance can be forced through when pressurized by the reducing volume imposed by the inflation of the second bladder. The benefit of the system is to avoid the waste of expensive therapeutic substances by filling an entire full length lumen with the substance in order to force it from the distal end of a delivery catheter. With the dual bladder delivery system, an inexpensive fluid can be used to occupy the space along the full length of the delivery catheter, yet its pressurization force can be applied to deliver a small quantity of the therapeutic substance maintained only at the distal end of the catheter.
Another feature of the present invention is a depth monitor, which may be applied to any of the above delivery catheters. The depth monitor uses changes in pressure being measured at the distal end of the catheter to signal the operator that the distal end of the catheter has been placed within myocardial tissue to a certain depth sufficient to implant the device. This depth monitoring is accomplished by providing one or a plurality of pressure ports at the distal end of the catheter that will be inserted into tissue in order to deliver the implant that it carries. The pressure port(s) are spaced a known distance from the distal end of the delivery catheter. The interior lumen of the catheter can transmit the pressure experienced at the distal end of the catheter through individual lumens to the proximal end where a pressure monitoring device for each pressure port is attached to the proximal end of the delivery device. When the distal end of the delivery catheter is in the left ventricle, pressure readings at the distal end will be dynamic. However, after the distal end of the delivery catheter enters the tissue to implant the device, the pressure ports become covered with surrounding tissue resulting in dampened or static signal. The most proximal pressure port when covered by the surrounding tissue, will likewise transmit a dampened signal and signals the operator that the distal end of the delivery catheter has been placed to a sufficient depth within the tissue to deliver the implant.
Another feature of the present invention is a navigation system utilizing magnetic fields transmitted over the body to identify the location within a patient of a catheter having sensing electrodes that interact with the electromagnetic coils. Computer software processes the information obtained from the magnetic pick-up coils and places the catheter on a virtual image of the heart to give the operator a general idea of where the catheter is located and what areas of ischemic tissue have been treated with implant devices. Because the delivery devices of the present invention are capable of delivering more than one implant to an area of ischemic tissue with one catheterization, a navigation system helping to guide the placement of the delivery catheter and implants is helpful.
It is an object of the present invention to provide an implant delivery system that is simple and effective to use.
It is yet another object of the present invention to provide an implant delivery system that is suitable for varying implant devices to the myocardium of the heart that will aid in revascularization of ischemic tissue.
It is yet another object of the invention to provide an implant delivery device that operates to grasp a tubular shaped implant by its inside surface so that the implant may be inserted into tissue.
It is another object of the invention to provide an implant delivery device that utilizes fluid pressure through the delivery catheter to insert the implant into the subject tissue.
It is yet another object of the invention to provide an implant delivery device that includes a dual bladder drug delivery system that reduces waste of expensive therapeutic substances in their application to a treatment site through a catheter.
It is still another object of the invention to provide a depth monitor capable of being associated with a delivery device that utilizes pressure sensed at the distal end of the catheter to reliably determine the location of the distal end of the device.
It is yet another object of the invention to provide a navigation system that is capable of identifying the location of a catheter delivering mechanical TMR inducing devices, within the human heart so that the catheter can be moved to various locations delivering multiple devices with one insertion into the heart.